Method for separating condensable substances from gases or gas mixtures

ABSTRACT

The present invention is a method for separating condensable substances from gases or gas mixtures with the use of porous materials including the steps of employing as adsorbents substances or materials suitable for capillary condensation and cyclically performing the method. The method can be used to separate water from air. The porous materials have a pore structure adapted to the environmental or climatic conditions present at the site of utilization of the method. The step of cyclically performing the method can be performing a plurality of times in succession separation by capillary condensation of the condensable substances in the porous materials and desorption of the condensed substances from the porous materials.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This is a U.S. National Phase application of PCT/EP99/08914 filed onOct. 28, 1999, which PCT application claims priority on DE applicationnumber 198 50 557.4, filed Nov. 3, 1998.

FIELD OF THE INVENTION

The invention relates to a method for separating condensable substancesfrom gases or gas mixtures. In particular for the separation of waterfrom air, with the use of porous materials.

BACKGROUND OF THE INVENTION

Many parts of the earth, especially arid regions such as the Sahelianzone or numerous torrid deserts located at a considerable distance fromthe sea, lack reserves of drinking water. Besides transporting drinkingwater, the only other possibility is to obtain it from moist air. Knownin this connection is the direct condensation of air below the dew pointand the adsorption of water from zeolites, active charcoal or silicagels, see for example DE-PS 2660 068. Water stored in this manner isextracted from the material by warming and then condensed.

The known methods are not particularly effective in terms of the actualyield of water since the regeneration of the moisture absorbed by thematerial must overcome high bonding energies or is solely oriented to adaily absorbent filling (see DE 44 30 901 C1 and EP 0003064 A1). Hereadsorption occurs mostly at night and desorption by day, with the airbeing heated directly by resorting to solar collectors or indirectlywith the use of heat accumulators. The recovery of water is thenconducted by day (EP 0003 964 A1) or at night using a cascade connection(DE 4430901 C1). A further known method for the expenditure of energy inthe regeneration of adsorbents is the utilization of electric energyusing wall grids or electrodes (DE 196 13 326 A1).

The Method of capillary condensation, long known from the relevantliterature (BRUNAUER, Stephen. et. al.: Some Remarks about CapillaryCondensation and Pore Structure Analysis. In: Journal of Colloid andInterface Science. Vol. 25, p. 353-358: KADLEC, O., DUBININ: M.M.:Comments on the Limits of Applicability of the Mechanism of CapillaryCondensation. In: Journal of Colloid and Interface Science, Vol. 31. No.4. Dec. 1969, p. 479-489) has so far only been employed for theextraction of solvents from gas (DE 2843416 A1. DE 196 13326 A1) withouttaking into account its existing potential for improved desorption.

SUMMARY OF THE INVENTION

The object of the present invention is to create a method for separatingcondensable substances from gases (and gas mixtures) which operates moreeffectively than the known methods.

The method according to the invention is characterized in that materialsor matter suited for capillary condensation are used which areparticularly suited to the climate (operating conditions) on site andwhich permit optimum regeneration yields. The special feature of theinvention thus lies in the selection of the appropriate material and itsinner structure. Instead of the previously used material, which wasbasically geared toward adsorption properties, a material is nowselected with which it is possible for so-called capillary condensationto attain high volume-specific yields by virtue of shorter regenerationcycles. This also results in matching the capillary structure of theadsorbent with the adsorbate and with the medium (gas) containing theadsorbate or with external conditions.

Condensation proceeds by capillary pressure due to the existing poreradii, with the inner capillary structure to be selected providing anoptimum volume-specific water bonding, for example, for thecorresponding climatic conditions and high yields through short-timeregeneration (more than 6 per night). The bonding forces to be overcomein the regeneration of moisture are thereby considerably weaker thanbinding by preceding adsorption or undefined capillary condensation. Therecovery of drinking water from air can be performed quite effectivelywith the new method and is no longer limited to a single regenerationper adsorption body and day. Other applications are also conceivable,such as the recovery of solvents.

Preferably a hydrophobing material is employed. This limits the uptakeof liquid by adsorption.

The material can be regenerated by using a combination of renewablesources of energy, such as solar energy, photovoltaics, wind energyand/or the supplementary storage of such energy with the appropriateaccumulators.

The material exhibits micropores and/or mesopores ranging in size from 4to 20 Angstrom units or from 20 to 500 Angstrom units, respectively. Itis advantageous to use a material having different pore sizes which areoptimally suited to the geographical site. In this manner, various airhumidities can be accounted for and the optimum conditions forregeneration can be established.

By carefully choosing the right material it is also possible to achievea selective separation of materials.

Other features of the invention are set forth in the claims and in theremaining description. In the following, the method will be furtherillustrated by example.

In a method for separating water from atmospheric air—in particular forthe recovery of drinking water—in a first phase a current of moist airfrom the atmosphere, in desert areas preferably at night, is conductedthrough a pack of microporous material in order to transfer the watermoisture contained in the air to the microporous material by means ofcapillary condensation. Suitable materials for use could be

ceramics,

activated charcoal,

activated alumina,

synthetic zeolites,

adsorber polymers,

adsorber resins,

molecular sieves,

silica gel,

cellulose materials,

compounds of the above substances and

mixtures of the materials.

The above materials can be employed inasmuch as they exhibit adistribution of pores and pore radii suitable for capillarycondensation. In particular, the respective mircopores and/or mesoporesof a particular size are present. For adapting to the climaticconditions in the Sahelian zone, approximately 60% of the materialexhibits pore radii of 40 to 200 Angstroms. The pore radii of theremaining material lie outside of these limits, but preferably between 4to 500 Angstroms.

In a second phase, the material is heated in order to vaporize thesubstance. For this purpose, in one embodiment an air current circulatedin a closed cycle is warmed with an air heater by means of previouslystored solar energy, or wind energy or by instantly generated wind orsolar energy, and passed through the pack filled with the material inorder to return to the microporous material the energy component whichhad been released during capillary condensation. In the process, thewater vapor bound to the material escapes and is absorbed by thecirculating stream of air. The air current thus saturated with watervapor is passed through a condenser contained in the cycle and the watervapor in the air is condensed out.

In another embodiment pursuant to the method according to the invention,the material is electrically heated for vaporizing the substance. Thisis possible through the use of an electronically conductive material,e.g. using electrically conducting ceramic as the adsorbent. Thematerial can be connected to a voltage source fed by stored solar power.The flow of current in the material can also be generated by induction.In any case, it is advantageous to employ a material with good thermalconductivity.

In another embodiment of the method according to the invention, thesubstance is heated in the material by microwaves and brought to thevaporization point. In this case, it is advantageous to use anon-metallic material.

Due to the optimum inner structure of the adsorbent material, adsorptionand desorption of the substance are preferably carried out in a cyclicalmanner, for example, multiple times during the night. Also possible andadvantageous is the execution of more than 6 cycles at night, with onlya portion of the overall adsorption and desorption being realized at anygiven time. Depending on the inner structure, this portion contains thelargest volume-specific water fraction. Thus more than 600 l of waterper ton of adsorbent can be recovered per night. The newly won substance(drinking water) is then available at the start of the day.

The recovery of water from an appropriate material (regeneration)requires considerably less adsorbent mass than is the case in thepresent method involving the desorption of water vapor from conventionalzeolites (appropriate for adsorption) or silica gels. In this respect,the material possesses a pore radii distribution which is defined andthus optimized for its particular application (temperature, humidity andair pressure at the site of water recovery).

The material is particularly available in the form of granulates,pellets or packing bodies of a defined structure. Other forms are alsopossible.

I claim:
 1. Method for separating a condensable substance from gases orgas mixtures with the use of a porous material comprising the followingsteps: a. employing a porous material having a pore structure which forcapillary condensation is adapted to (i) the environmental or climaticconditions present at the site of utilization (ii) the condensablesubstance, and (iii) the gases or gas mixtures containing thecondensable substance; and b. cyclically performing said method until atleast a portion of overall adsorption and desorption is realized byperforming a plurality of times in succession separation by capillarycondensation in the porous material and desorption of the condensedsubstance from the porous material; wherein the separation by capillarycondensation in the porous material and desorption of the condensedsubstance from the porous material are performed only in a region ofcapillary condensation.
 2. Method according to claim 1, whereincyclically performing said method of step (b) continues until theoverall adsorption and desorption is entirely realized.
 3. Methodaccording to claim 1, wherein the porous material has micropores and/ormesopores.
 4. Method according to claim 1, wherein the porous materialis a hydrophilic material.
 5. Method according to claim 1, wherein theporous material comprises granulates, pellets, or packing bodies ofdefined structure.
 6. Method according to claim 1, wherein capillarycondensation and subsequent regeneration occur cyclically at night, orcapillary condensation occurs at night and regeneration by day. 7.Method according to claim 1, wherein for separating water fromatmospheric air, in a first phase a current of cool, moist air from theatmosphere is conducted through a pack with microporous or mesoporousmaterial in order to transfer the water moisture contained in the air tothe material by means of capillary condensation, that in a second phasean air current is warmed by an air heater by means of in particularpreviously stored solar energy or wind energy or by directly generatedsolar or wind energy and passed through the pack filled with thematerial in order to transfer the water vapor bound in the material tothe air current, and that finally the air current thus saturated withwater vapor is passed through a condenser and the water vapor in the airis condensed out.
 8. Method according to claim 1, wherein the porousmaterial is electrically conductive or has electric conductors. 9.Method according to claim 8, wherein the desorption of the condensedsubstance from the porous material results from electric heatingoccurring in the porous material.
 10. Method according to claim 1,wherein the desorption of the condensed substance from the porousmaterial occurs by heating one or both the condensed substance and theporous material by means of microwaves.
 11. Method according claim 1,wherein approximately 60% of the porous material exhibits pore radiibetween approximately 40 and 200 angstroms, and that the remainingporous material exhibits different pore radii.
 12. Method accordingclaim 1, wherein approximately 60% of the porous material exhibits poreradii between approximately 40 and 200 angstroms, and that the remainingporous material exhibits pore radii between approximately 4 and 500angstroms.
 13. Method according to claim 1, wherein the porous materialis a hydrophobic material.
 14. Method for separating a condensablesubstance from gases or gas mixtures with the use of a porous materialcomprising the following steps: a. employing a porous material having apore structure which for capillary condensation is adapted to (i) theenvironmental or climatic conditions present at the size of utilization(ii) the condensable substance, and (iii) the gases or gas mixturescontaining the condensable substance; and b. cyclically performing saidmethod until at least a portion of overall adsorption and desorption isrealized by performing a plurality of times in succession separation bycapillary condensation in the porous material and desorption of thecondensed substance from the porous material; wherein the separation bycapillary condensation in the porous material and desorption of thecondensed substance from the porous material are performed only in aregion of capillary condensation; the portion of the overall adsorptionand desorption realized depending on an inner structure of the porousmaterial—containing the largest volume-specific fraction of condensablesubstance.
 15. Method for recovering water from air with the use of aporous material comprising the following steps: a. employing a porousmaterial having a pore structure which for capillary condensation isadapted to (i) the environmental or climatic conditions present at thesite of utilization (ii) water, and (iii) the air containing the water;and b. cyclically performing said method until at least a portion ofoverall adsorption and desorption is realized by performing a pluralityof times in succession separation by capillary condensation in theporous material and desorption of the water from the porous material;wherein only short-time regenerations are performed, with the separationof water from air being conducted a number of times during the night.16. Method according to claim 15, wherein the separation of water fromair is conducted with more than six cycles in one night.
 17. Methodaccording to claim 15, wherein cyclically performing said method of step(b) continues until the overall adsorption and desorption is entirelyrealized.
 18. Method according to claim 15, wherein the porous materialcomprises granulates, pellets, or packing bodies of defined structure.19. Method according to claim 15, wherein the separation by capillarycondensation in the porous material and desorption of the condensedsubstance from the porous material are performed only in the region ofcapillary condensation.